This invention relates to a slip joint for mounting a heat exchanger relative to a gas turbine. In particular, it relates to a slip joint between the exhaust gas manifold and the hot air inlet duct of an associated heat exchanger.
The use of gas turbine engines in stationary power applications and in ground moving vehicles where the power/weight factor is not critical permits the inclusion of a heat exchanger for heating incoming air with the heat of the engine exhaust gasses. Since gas turbine engines operate most efficiently at higher temperatures, preheating the intake air prior to injecting fuel results in a higher output efficiency per pound of fuel burned. Therefore, with the inherent characteristic of high exhaust gas temperatures in gas turbine engines, it has become common, when weight is not a critical factor, to add a heat exchanger to extract excessive heat from turbine exhaust gasses and heat the inlet gasses of the engine. To increase efficiency even further, it is normal procedure to heat the inlet gasses subsequent to compression thereof. Thus, the inlet gasses are ducted from the compressor section of the engine casing through a heat exchanger and then returned to the engine in the vicinity of the engine combustor through a second duct. A third duct interconnects the exhaust manifold of the engine to the heat exchanger. An example of the heat exchanger contemplated for use in this type of engine is described in U.S. Pat. No. 3,759,323.
The material used for construction of the heat exchanger and the material used for construction of the engine generally will have different thermal expansion characteristics. Accordingly, one of the problems in designing a heat exchanger for a gas turbine engine and an associated mounting system therefor, is to overcome the problems inherent in different thermal expansion rates for the two components. In order to increase efficiency in the system, it has been found appropriate to mount the heat exchanger immediately adjacent to the engine, generally above the engine. A typical mounting for heat exchanger adjacent the engine is disclosed in copending application, Ser. No. 728,669, assigned to the assignee of this invention. The mounting means disclosed therein has proved satisfactory for use in higher horsepower engines wherein thermal expansion problems increase, particularly in relation to the interconnecting manifolds between the heat exchanger and the engine. In the structure disclosed in the above-mentioned mounting means, translatory movement between the heat exchanger and the engine generally occurs at two of the three manifolds, either laterally or vertically relative to the engine. The third manifold, generally the center or engine intake manifold, is adapted to allow rotational movement only; therefore, motion in the other two manifolds is generally in opposite directions as the temperature increases or decreases. The aforesaid U.S. patent application, Ser. No. 728,669, adequately provides for a flexible cool air inlet duct and a rotatable hot air outlet duct from the heat exchanger for the air provided from the engine compressor. The exhaust gas duct communicating hot exhaust gasses from the engine to the heat exchanger provides special problems. In addition to a requirement for a seal in the joint, the varying thermal expansion mentioned previously must also be allowed for. The thermal expansion occurring in this joint utilizing the aforedescribed mounting scheme results in translatory motion of the heat exchanger relative the engine, thus too tight a clamp defeats the purpose of the joint while too loose a clamp allows for loss of exhaust gasses through the joint itself.